1. Field of the Invention
The present invention relates to a pattern forming method of transferring a fine concavo-convex pattern formed in a mold to a transferred substrate, and also relates to a mold using the same.
2. Description of the Related Art
In recent years, in integrated circuits the reduction in size and higher integration has been progressing, and as a pattern transfer technique for realizing this fine processing, higher precision of the photolithography apparatus has been pursued. However, the processing method is approaching the wavelength of a light source of light exposure and the lithography technology is also approaching the limit. For this reason, for pursuing further reduction in size and higher precision, an electron beam lithography apparatus which is a type of a charged particle beam apparatus is used in place of the lithography technology.
The pattern formation using an electron beam employs a method of drawing a mask pattern, unlike the one-shot exposure method in the pattern formation using a light source, such as an i line or an excimer laser. Therefore, the more patterns to draw, the more exposure (drawing) time it takes and the more pattern formation time it takes, which is a disadvantage. For this reason, as the integration level increases exponentially from 256 mega, to 1 giga, to 4 giga in memory capacity, the pattern formation time also increases exponentially, and thus a significant degradation in throughput is a concern. Then, for the purpose of speed up of the electron beam exposure apparatus, a collective pattern irradiation method has been under development where various shapes of masks are combined and these masks are irradiated with an electron beam to thereby form an electron beam of a complicated shape. As a result, while the reduction in pattern size is progressing, an increase in size and complexity of the electron beam lithography apparatus becomes essential, thus causing a disadvantage of increasing the apparatus cost.
On the other hand, as a technique for forming fine patterns at low cost, a nano imprint technique is known where a predetermined pattern is transferred by die-pressing a mold (metallic mold) having concavity and convexity of the same pattern as the pattern, the pattern being desired to be formed on a substrate, against a resin film layer formed in the surface of a transferred substrate. It is disclosed that the nano imprint technique allows a fine structure of 25 nm or less to be formed by transcription using a silicon wafer as a metallic mold.
In forming a fine pattern, such as an integrated circuit, a precise alignment needs to be carried out between a reticle having, for example, an original picture pattern (transcription pattern) formed thereon after precisely detecting the pattern position of a substrate which is placed on a stage. For the alignment accuracy, much higher alignment accuracy is needed due to reduction in pattern size associated with higher integration of semiconductor devices. For example, in order to form a pattern of a 32 nm node, a precise alignment with an error of 10 nm or less is required.
On the other hand, in the patterned media known as one of the next generation large capacity magnetic recording media, a fine concavo-convex pattern is formed in the recording surface of a disc substrate. In a commercially available ordinary disc substrate, a hole for fixing to a rotating drive part is formed in the center of the substrate, and the disc substrate rotates about the center of this hole, the center being as an axis. For this reason, concavo-convex patterns are arranged on circumferences concentric to the hole in the center of the substrate. If circular patterns of 10 nm in diameter are arranged so that the pitch interval (center to center distance between adjacent circular patterns) becomes 25 nm, then a recording medium with a recording density of 1 tera bit/square inch may be formed.
In JP-A-2003-157520, a nano imprint technique is used in forming a resist pattern for a magnetic recording media. In arranging fine concavo-convex patterns onto circumferences concentric to the rotation center of a disc substrate using the nano imprint technique, a relative alignment between a mold and the disc substrate becomes important. As the alignment means between the mold and the disc substrate, in JP-A-2003-157520, an alignment pattern is also formed along with a fine concavo-convex pattern onto a transferred substrate using a nano imprint technique, and subsequently, a rotation central axis is determined using the alignment pattern. In JP-A-10-261246, alignment is carried out by attaching to the center of a mold a projection of approximately the same diameter as the hole diameter in the center of the disc substrate, and fitting the disc substrate into the projection. JP-A-2001-325725 discloses a technique concerning the alignment of a perforated magnetic recording medium. In this method, an alignment mark is formed in the center of a master disc, and the alignment mark in the center of the master disc is shot by a CCD camera through a central opening of the disc substrate, and a relative alignment is carried out.